Leaking petroleum from underground storage tanks (USTs) is one of the biggest threats to groundwater quality in the US. Currently, there are approximately 597,000 federally-regulated active USTs at about 215,000 sites in the US. It was estimated that 680,000 USTs are expected to require remediation under federal regulations over the next few decades, with average cleanup costs reaching almost $125,000 per site. Leaking USTs account for over 40% of US soil and groundwater remediation market, the latter posted revenues of about $8.1 billion in 2004 and an estimated market of $13 billion by 2010. BTEX (benzene, toluene, ethylbenzene and xylenes) are the major aromatic components frequently found in groundwater as a result of leak in USTs. BTEX are classified as priority pollutants regulated by the US Environmental Protection Agency (EPA) and were among the target compounds toward EPA's 33-50 program. Benzene is also ranked #6 in the ATSDR 2011 Substance Priority List. Benzene is teratogenic and may be associated with the development of leukemia, and toluene is a suspected depressant of central nervous system. Because of these health concerns, the maximum levels in potable water are 0.05, 1, 0.7 and 10 ppm for benzene, toluene, ethybenzene and xylenes, respectively. Among all remediation technologies for treating BTEX-contaminated groundwater, bioremediation appears to be an economical, energy-efficient and environmentally sound approach. However, additional electron acceptor is usually required to accelerate the process. Aerobic remediation is regarded as the fastest process but usually leads to loss of volatile organic compounds into air instead of complete BTEX removal associated with high capital and operational cost due to the oxygen injection system. Anaerobic process is limited in biodegradation efficiency and usually requires addition of either nitrates or sulfates as electron acceptors which significantly increase the total cost. This project proposes to remove BTEX from groundwater in a novel bio-electrochemical system (BES) while simultaneously generating methane. The benefits of this technology are: (i) more efficient due to bio- electrochemical stimulation and improvement; (ii) more cost effective due to lack of additional electron acceptor; (iii) more sustainable as most carbon is captured as methane. Phase I will focus on demonstrating biodegradation of BTEX in BES. Phase II will work on system optimization, scale up and pilot demonstration. The end goal for Phase I and Phase II R&D will be a BTEX contaminated groundwater remediation system that is: (i) with high treatment efficiency; (ii) with lower cost; (iii) robust system by incorporating electrochemical signals; (vi) green remediation technology with significantly smaller carbon footprint.